Organophilic clays are widely used as rheological control agents in a wide variety of solvent systems. In particular, organophilic clays have found wide usage in wellbore fluids, used in operations related to the development, completion and production of natural hydrocarbon reservoirs. Typical operations include drilling, fracturing subterranean formations, modifying the permeability of subterranean formations, logging operations, sand control, packer fluids, etc.
In particular, in deep well drilling, the use of organophilic clays in oil-based muds have certain advantages despite their considerably higher initial cost. The advantages of oil-based fluids are apparent in water-sensitive formations, e.g., swelling shale, insoluble salt formations, and at high temperatures. These fluids are used for drill stem lubrication, particularly in drilling curved or deviated wells, for corrosion protection and they have the further advantage of being reusable.
One of the primary functions of organophilic clays in oil-based wellbore fluids, as well as other non-aqueous based fluids (i.e glycol ethers), is to act as viscosifiers. However, it is well known that for organophilic clays to swell in or viscosify a non-aqueous wellbore fluid it is usually necessary to use small amounts of polar molecules as activators. Typical activators for use with clay-type thixotropic viscosifying agent such as organophilic clays include water, ethanol, methanol, glycols, sodium silicate, sodium fluoride, magnesium silico fluoride, calcium carbonate, polar aprotic compounds, etc. An especially preferred and widely used activator is propylene carbonate.